塔里木盆地塔中——顺托果勒地区奥陶系良里塔格组碳酸盐岩颗粒滩沉积特征

Sedimentary Characteristics of Carbonate Shoals of Ordovician Lianglitage Formation in Tazhong and Shuntuoguole Area,Tarim Basin

塔中—顺托果勒地区奥陶系颗粒滩具有良好的油气资源前景。本文介绍了碳酸盐岩颗粒滩的定义和研究概况。通过镜下薄片分析将该地区良里塔格组碳酸盐岩颗粒滩主要划分为3类,并明确了3类颗粒滩的微观沉积特征。颗粒滩主要类型为:内碎屑滩、生物碎屑滩和鲕粒滩,所含的主要颗粒类型分别是内碎屑(砂屑为主,含砾屑)、生物碎屑和鲕粒,多为亮晶胶结,反映了高能水动力环境,由于迁移作用颗粒时常会相互伴生。另外,也发现了在低能环境中发育的复鲕和中—高能水动力环境下的藻粒;藻粒常常会与内碎屑颗粒、生物碎屑颗粒伴生,规模不大,多形成于中—高能水动力环境下的碳酸盐岩潮坪环境或台缘缓坡带。通过连井对比分析可以得出,良里塔格组可以划分为3个三级层序,海侵体系域主要以薄层退积为主,高位体系域以厚层加积为主。最后,本文结合颗粒滩的展布特征建立了该地区良里塔格组颗粒滩沉积模式。

The Ordovician carbonate shoals in Tazhong and Shuntuoguole area have good prospects for hydrocarbon resources.The definition and classification of carbonate shoals are clarified in this paper.Based on the analysis of thin sections,the carbonate shoals of Lianglitage Formation could be classified into three types:intra-clastic shoal,oolitic shoal and bioclastic shoal,containing mainly intra-clast,bioclast,and ooid.Most of the carbonate shoals are bright crystal cement,reflecting a high-energy hydrodynamic environment.Different grains are often associated with each other because of migration.The compound ooid developed in low energy environment and the algae grain from middle-high energy environment are also identified.Algae grains are developed usually together with intra-clast and bioclast,although not abundant,and formed in a middle-high energy tidal flat environment and gentle slope of carbonate platform.The cementation type,separation and grinding are affected by the energy of sedimentary environment and hydrodynamic conditions.Through the comparison analysis of connecting wells,Lianglitage Formation could be subdivided into three third-order sequences.The stacking pattern of carbonate shoals in transgressive system tract is thin-layer cake retrograde deposit,while in high system tract that is thick-layer cake deposit.At last,the sedimentary model of carbonate shoals in this area is built through combining their distribution characteristics.